The present invention relates to an optical disk device which can read and replay data from an optical disk upon which data is recorded at a variable bit rate for each sector.
Super Video CDs (hereinafter “SVCDs”) are a type of media package distributed in various Asian countries. AV data (an MPEG program stream) is recorded upon an SVCD sector by sector, encoded using the MPEG2 (Moving Picture Experts Group 2) method, which is a variable bit rate compression encoding method.
An optical disk device which replays this type of media package is provided with a function for displaying, during the replay of AV data, a replay elapsed time which corresponds to the current replay position. This replay elapsed time is the time period which would be required for normal replaying of the AV data from its start to the present replay position. The correlation relationship between this replay elapsed time and the address of the sector which is currently being replayed will now be described in detail in the following.
First, as a preliminary, the correlation relationship between the address of the sector which is currently being read and the address of the sector which is currently being replayed will be explained. While reading out of AV data upon an optical disk is being performed, generally pre-read processing is performed. This pre-read processing is processing for reading out in advance, from the optical disk, AV data subsequent to the address where the AV data that is currently being replayed is located, and for storing this data in a buffer memory. This AV data which has been temporarily stored in the buffer memory is subsequently sequentially decoded and replayed. Here, the buffer memory is provided in order to prevent underflow of the AV data occurring (underflow may be caused by the decoding processing). And, due to the delay in this buffer memory, the address of the sector which is currently being replayed and the address of the sector which is currently being read come to be different. Because of this, the correlation relationship between the address of the sector which is currently being read and the address of the sector which is currently being replayed is indeterminate.
Next, with a Video CD upon which AV data has been encoded according to MPEG1, since MPEG1 has a fixed bit rate, the replay elapsed time and the address of the sector which is currently being replayed correspond one-to-one. Due to this, even though there is a delay time due to the buffer memory described above, still the optical disk device is able to ascertain the address of the sector which is currently being replayed accurately from the replay elapsed time, in a simple and easy manner. Because of this fact, in MPEG1, if a command for fast forward is issued, fast forwarding can be easily executed by taking the address of the sector which is currently being replayed as a starting point. Similarly, if a command for fast reverse is issued, fast reversing can be easily executed by taking the address of the sector which is currently being replayed as a starting point. Here, fast forward means a fast replay at high speed where the replay speed is higher than that of normal replay. Moreover, fast reverse means a fast replay at high speed in the opposite direction to the direction in which normal replay is performed, and moreover where the replay speed is higher than that of normal replay. Hereinafter, the term “special replay” will be used generically for fast forward replay, for slow forward replay, or for reverse replay.
It should be understood that, in Japanese Laid-Open Patent Publication 2002-150691, a replay device is proposed which calculates the replay elapsed time and the remaining time for replay.
However, with an SVCD upon which AV data encoded according to MPEG2 is recorded, the data is recorded at a variable bit rate. Due to this, the replay elapsed time and the address of the sector which is currently being replayed do not correspond one-to-one. In other words, the correlation relationship between the replay elapsed time and the address of the sector which is currently being replayed is indeterminate.
Because of this fact, with a prior art optical disk device, it has not been possible to know the address of the sector which is currently being replayed. Thus, with a prior art optical disk device, if a command is issued for some type of special replay such as fast forward or fast reverse or the like, it has not been possible to determine an appropriate starting point, since the address of the sector which is currently being replayed, which should be the starting point, is not known. Because of this problem, with a prior art optical disk device, irrespective of whether the user has issued, for example, a fast reverse command, it sometimes happens that data which is temporally subsequent to the point which is currently being replayed, is replayed, which is undesirable. Accordingly, with a prior art optical disk device, when special replay of some such type is to be performed, the user has sometimes experienced an undesirable sense of discomfort.
Thus, the object of the present invention is to provide an optical disk device which can execute special replay by accurately calculating the address of the sector which is currently being replayed, so that the reliability when performing such special replay is enhanced.